This application claims the benefit of PCT/IN01/00092, in the name of Ashwin Champraj Shroff, entitled xe2x80x9cA Process For The Stereoselective Preparation Of Insecticide 6,7,8,9,10-10-Hexahalo-1,5,5A,6,9,9A-Hexahydro-6,9-Methano-2,4,3-Benzodioxathiepin-3-Oxide,xe2x80x9d filed on Apr. 24, 2001.
A process for the stereoselective preparation of insecticide 6,7,8,9,10,10-hexahalo-1,5,5a,6,9,9a-hexahydro-6,9-methano-2,4,3-benzodioxathiepin-3-oxide.
6,7,8,9,10,10-hexahalo-1,5,5a,6,9,9a-hexahydro-6,9-methano-2,4,3-benzodioxathiepin-3-oxide are of the formula I: 
wherein X may be a halogen such as fluorine, chlorine or bromine.
U.S. Pat. No. 2,799,685 describes unsaturated polycyclic sulfites of the general formula II: 
wherein X may be hydrogen or halogen or alkyl group and Y may be hydrogen or alkyl group, and their derivatives containing two hydrogen atoms in 5,6-positions. These compounds are reported to exhibit insecticidal activity. The process for the preparation of these compounds comprises heating a diol of the general formula III: 
wherein X and Y are each as defined above, with thionyl chloride under heating optionally in an inert organic solvent. The product is reported to be a mixture of two isomers. The desired isomer may be resolved from the mixture, for instance by fractional crystallisation using petroleum ether.
U.S. Pat. No. 3,251,856 describes a process for the resolution/separation of the two isomers viz xcex1 and xcex2-isomers of 6,7,8,9,10,10-hexahalo-1,5,5a,6,9,9a-hexahydro-6,9-methano-2,4,3-benzodioxathiepin-3-oxide, commonly known as endosulfan of the formula IA: 
The resolution process comprises contacting the endosulfan isomeric mixture with a halogenated hydrocarbon solvent at 40-50xc2x0 C. followed by cooling the mixture to 20-25xc2x0 C. The resulting insoluble portion in the mixture is reported to predominantly contain the high melting isomer viz xcex2-isomer of endosulfan whereas the solution portion when subjected to evaporation results in a residue which is reported to predominantly contain the low melting isomer viz xcex1-isomer of endosulfan. The xcex1 and xcex2-isomers so obtained may be purified by crystallisation from alcohol.
Both the isomers of endosulfan are reported to exhibit different insecticidal properties. For instance, in short exposure periods, xcex1-endosulfan is more effective against flies than xcex2-endosulfan. In the case of fruit flies Drosophila melanogaster, the killing times (LT50) with the use of xcex1-endosulfan and xcex2-endosulfan are in the ratio 1:3 respectively. Insecticidal effectiveness or efficacy of xcex1-endosulfan against wood boring insects is more as compared to xcex2-endosulfan. Insecticidal effectiveness limit per m3 wood with the larvae of the house longhorn beetle Hylotupes bajulus L is more in the case of xcex2-endosulfan as compared to xcex1-endosulfan (Mater. Org. 1983, 18(2), 81-91, Kuelune Helmut et al; CA 100: 134245a). Both the isomers differ in insecticidal persistence and biodegradability. xcex1-Endosulfan decomposes rapidly by soil microorganisms when compared to xcex2-endosulfan (Karachi Univ J. Sci; 1985, 13(2), 191-7, Akhtar Shahida et al; CA 107: 91836u). xcex1-Endosulfan is degradable by both bacteria and fungi, whereas xcex2-endosulfan is degradable mainly by bacteria (Int. J Environ. Stud, 1981, 16 (3-4), 171-80, El Beit, I O D et al; CA 94: 151865c). xcex2-endosulfan has greater half life than xcex1-endosulfan under varying environmental conditions (J. Environ. Sci. Health, Part B, 1995, B30 (2), 221-32, Ceron J J et al; CA 122: 180980p). Therefore, treatment with xcex2-endosulfan is particularly preferred to achieve desired efficacy over a long term.
The xcex1 and xcex2-isomers of endosulfan are reported to be obtained in the average isomeric ratio of about 2:1 (U.S. Pat. No. 3,251,856). Due to the different in the physical, chemical and biological properties of xcex1 and xcex2-endosulfan and xcex1 and xcex2-benzodioxathiepin compounds in general, it is advantageous to have increased quantity of the desired stereoisomer in the isomeric mixture depending upon the intended specific application of the benzodioxathiepin compound. In order to obtain required quantity of a desired isomer of the benzodioxathiepin compound, correspondingly large quantities of the substrate viz the diol compound is required. Therefore, the above process is uneconomical. Besides, it also generates the undesired isomer in the ratio 2:1 and its efficiency is low.
An object of the invention is to provide a process for the stereoselective preparation of 6,7,8,9,10,10-hexahalo-1,5,5a,6,9,9a-hexahydro-6,9-methano-2,4,3-benzodioxathiepin-3-oxide having insecticidal activity, which results in increased quantity of the desired stereoisomer in high purity without using additional quantity of starting material.
Another object of the invention is to provide a process for the stereoselective preparation of 6,7,8,9,10,10-hexahalo-1,5,5a,6,9,9a-hexahydro-6,9-methano-2,4,3-benzodioxathiepin-3-oxide having insecticidal activity, which is economical.
Another object of the invention is to provide a process for the stereoselective preparation of 6,7,8,9,10,10-hexahalo-1,5,5a,6,9,9a-hexahydro-6,9-methano-2,4,3-benzodioxathiepin-3-oxide having insecticidal activity, which is efficient.
Another object of the invention is to provide a process for the stereoselective preparation of 6,7,8,9,10,10-hexahalo-1,5,5a,6,9,9a-hexahydro-6,9-methano-2,4,3-benzodioxathiepin-3-oxide having insecticidal activity, without using any foreign reagent which may introduce impurity to the product.